PROSTAGLANDIN E-1 ANTAGONIZES HYPOXIC PULMONARY VASOCONSTRICTION BUT REDUCES SYSTEMIC BLOOD-PRESSURE IN DOGS

Objective: To investigate whether prostaglandin E-1 (PGE(1)) directly inhibits hypoxic pulmonary vasoconstriction in dogs. Design: Prospecti ve, longitudinal study. Setting: University research laboratory. Subje cts: Six mongrel dogs in vivo. Interventions: The left thorax of anest hetized and ventilated dogs was opened and the left lower lobe was sep arately ventilated, The tip of the thermodilution pulmonary artery cat heter was introduced into the left lower lobe pulmonary artery, The le ft lower robe was ventilated with hyperoxic (95% oxygen and 5% CO2) or hypoxic (95% nitrogen and 5% CO2) gas. By manipulating the occluders placed on both pulmonary arteries, blood flow in the left lower lobe w as regulated, Continuous pressure-flow plots for the left lower lobe w ere then obtained, Measurements and Main Results: Measurements include d continuous pressure flow plot generation, thermodilution cardiac out put and blood flow in the left lower lobe, and blood gas analysis, Alv eolar hypoxia of the left lower lobe caused blood flow in the left low er robe to decrease from 371.8 +/- 63.4 to 95.0 +/- 23.4 mL/min and sh ifted the pressure-flow plot to the right, with a decreased slope and with an increase in the pressure axis intercept, Subsequently, systemi c venous infusion of PGE(1) at a rate of 0.3 mu g/kg/min had no effect on the pressure-flow plot configuration, blood flow in the left lower lobe, pulmonary vascular resistance, systemic vascular resistance, an d Pao(2). However, there was a decrease in the pressure-axis intercept of the pressure flow plot, Infusion of PGE(1) at a rate of 3.0 mu g/k g/min (high-dose) during hypoxia reduced pulmonary vascular resistance and systemic vascular resistance by 19% and 25%, respectively, and re turned the pressure flow plot toward normal while blood flow in the le ft lower lobe increased to 122.6 +/- 21.0 mL/min. Consequently, Pao(2) decreased from 270 +/- 31 to 144 +/- 32 torr (36.0 +/- 4.1 to 19.2 +/ - 4.3 kPa). Conclusion: High dose PGE(1) essentially inhibits hypoxic pulmonary vasoconstriction, at the expense of a deterioration in pulmo nary gas exchange and systemic blood pressure in dogs.